The conventional vertical bipolar junction transistor (BJT) cannot isolate fully form the substrate or the well region, which may lead to undesired carrier injected to the substrate and parasitic BJT. In view of this problem, a deep buried layer, usually, is then formed to surround fully the vertical BJT to improve the isolation performance. However, such solution needs extra masks and more complicated process, making high manufacturing cost.
In light of foregoing, there is a need in the art to not only reduce the manufacturing cost but also to raise the current gain of BJT.